Coupling for wave guides



Aug. 14, 1951 L. HOCHGRAF 2,564,007

COUPLING FOR WAVE GUIDES Filed NOV. '14. 1947 CONDUCT/NG fou/0 /A/l/E/vro@ y l.. HOCHGRAF p/MmejfM A TTOR/VEV atentec ug. 14, l:1.951

ooUPLING FOR WAV-E GUIDES e A'Lester Hochgraf, Maplewood, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application November 14, 1947, Serial No. 785,890

6 Claims.

systems and more particularlyto, couplings for Wave guides for transmittingv high frequency electromagnetic waves. A

An object of this invention is to reducev the reiiection of transmitted energy at the joint between two sections of a wave guide.

Another object of this invention is `to join sections of wave guide or similar structure by a coupling which has relatively low transmission losses.

Accordingly, this invention provides a coupling or joint between two sections of wave guide hav-v ing identical cross sections, this couplingbeing made up of a quantity of conducting liquid constrained to a form providing an inner wall continuous with the walls of the guide by a low-loss thin-walled dielectric tube having its ends inserted in the adjacent ends of the wave-guide sections and in slidable relation with one of said sections. The conducting fluid is maintained around the dielectric tube by a jacket, also in slidable relation with one of said sections, enclosing a portion of the ends of the sections.

The various features of this invention will bev better understood from the following detailed description when considered in conjunction with the accompanying drawings in which:

Fig. 1 discloses a sectional view of a coupling for wave-guide sections illustrative of one embodiment of the invention;

Fig. 2 is a cross section of the coupling of Fig. 1 taken along the line 2-2 of Fig. 1 and Fig. 3 is a cross section of a modification of the coupling of Fig. l in which the wave guides and coupling are circular, the section being taken along a line corresponding to 2 2 of Fig. 1.

Referring to the drawing, a portion of an electromagnetic transmission system including the coupling of this invention and a part of two rectangular wave-guide sections Ill and II are shown. Suitably secured within section I is a thin-walled low-loss dielectric tube I2 of suitable material, for example, polystyrene, having outer dimensions substantially equal to the inner di-v mensions of the wave guide. The length of this dielectric tube I2 is considerably longer than the maximum extension for which the particular coupling is constructed. The tube I2 extends from section IEl into section II in close ltting slidable relation with the interior of said section II. The ends I3 and I4 Aof tube 1.2 are tapered in order to provide a gradual l.transition of the dielectric within the interior of the wave-guide system across the coupling from that of all air to that of air and the material of the tube. This gradual transition of the dielectric interior of the wave guide has been found to lbe a very satsfactory means of providing for the gradual change in impedance which, if abrupt, would pro,- duce transmission losses across the joint.

The coupling is encased by a tubular member I5 which is constricted at I6 and is secured by some suitable means to the exterior of section Ill. This casing I5 extends across the gap l1 between the sections and beyond a distance cie-l termined by the extension for which the coupling is constructed but in any event approximating the distance that the dielectric tube I2 extends within section II. A guide ring I8 is secured within the casing I5 at its end I9. This ring has an inner dimension substantially equal to the outer dimensions of the section II and is ar. ranged so that the surface 20 of its inner surface will slide over the outer surface of section II. Thus, the ring I8 in cooperation with theV dielectric tube I2 forms a support which maintains section II in axial alignment with section Ill throughout any relative movement between the sections. A circular wave guide and joint as shown in Fig. 3 permits rotary as well as axialA movement.

The gap I'I between the sections In and II is' bridged electrically by a conducting liquid 2I which is confined therein by the enclosure formed' by the outer walls of the dielectric tube I2 and the wave Iguide sections III and I I in cooperation with the casing I5 surrpunding these portions. In order to provide a smooth continuous conducting surface comprisedA of the inner wall of section ID, the liquid across the gap, and the inner wall of section II, it is necessary to reduce to a minimum any meniscus in the conducting liquid which might appear at the edges 22 and 23 of the sections; therefore, the edges of the sections are beveled as shown in the drawings and are of such material as will be wetted by the liquid. Since it is necessary that the dielectrictube slides freely within the section II without the liquid leaking at this point a close fit is necessary be tween the dielectric tube and the Wave guide; if.. the dielectric and the inner conductor surface over which it slides are of such material as will` not vbe wetted by the liquid, the fit between theY tube and the conductors can be considerablylooser than it need be otherwise to maintain ya',`-

leakproof fit.

As one embodiment of this invention, it is contemplated coupling guide sections of brass or ccpper by a liquid section of mercury. Since mercury will amalgamate with either copper or brass,= weakening the structure of the metal and conf taminating the mercury so that it readily oxifv dizes when exposed to air to form a semisolid substance, it is obvious that the copper or brass must be protected from the mercury. It is also desirable that no surfaces of the guide sectionsV which are contacted by the mercury except the Vedges 22 and 23 be wetted thereby. A satisfacguide sections can be kept from contact with thev mercury by using a lacquer or other non-metallic covering which mercury does not wet. In order to further protect the wave-guide sections, it has been found advisable, especially where the lacquer covering is exposed to any abrasive effects such as that of the dielectric liner sliding over the interior of section Il and that of the ring I8 sliding over the exterior of section l I, to provide an inner coating such as a dense nonporous plating of Yiron which mercury will not attack even though the lacquer coating is scratched or Worn in use. The use of stainless steel as the material of the outer casing I5 and the ring I8 eliminates any diiiiculty as to amalgamation and wetting and provides a strong reinforcing member maintaining the alignment of wave-guide sections I and Il.

The use of this coupling requires that a quantity of conducting liquid be maintained within the casing l sucient to cover the portion of the dielectric tube l2 exterior of the wave-guide sections at all degrees of extension or contraction. This can be done in a vertical joint as shown in the drawing by constructing the outer jacket with a capacity for such an amount of liquid, that when the joint is at its greatest extension, the level of the liquid remains above the edge 23 and at its minimum extension, the level of the liquid is below the ring I8. In a horizontal joint, however, either the upper side of the jacket must be enlarged to form a liquid reservoir or a separate reservoir is necessary in order to supply enough liquid so that at the greatest extension of the joint, the liquid surface is above the upper side of the dielectric tube I2.

In practice, it has been found that the introduction of a thin-walled, tapered-end, low-loss dielectric tube as described causes very little change in the impedance within a wave guide, and that the use of a section of guide wall having a considerably greater resistivity than that of the major portion of the guide, as when mercury is used across the gap between the two copper sections, has practically no effect on the transmission of the system and very little change of impedance within the guide. Thus a coupling is provided having highly satisfactory electrical characteristics which joins two sections of a wave guide so that at all extensions of the wave guide, a. continuous inner conducting surface is provided allowing movement as would be necessary, for example, in a long run of wave guide where means must be provided for expansion and contraction, or where adjustments of the length of the wave guide are necessary to achieve the desired operating characteristics.

As many possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A Wave-guide coupling for a pair of spaced wave guide sections comprising a dielectric member tted within the adjacent ends of said sections in fluid-tight relationship therewith, and a' quantity of electrically conductive fluid maintained around the portion of said dielectric member exterior of said guide sections.

2. A wave-guide coupling for a pair of spaced axially aligned wave-guide sections comprising a low-loss dielectric liner closely fitted into the adjacent ends of said sections, a jacket surrounding the adjacent ends of said sections and the exposed portion of said liner, and a quantity of conductive fluid contained in said jacket Sullicient to cover the exposed portion of said liner and the ends of both wave-guide sections Whereby the electrical continuity of the inner conducting surface of the guideis maintained.

3. A wave-guide coupling for a pair of spaced wave guide sections comprising a low-loss dielectric liner closely fitted into the adjacent ends of said sections and having its ends tapered, a jacket enclosing the adjacent ends of said sections and the exposed portion of said dielectric liner, and a quantity of conductive-fluid contained in said jacket sufficient to cover the exposed portion of said liner and the ends of both wave-guide sections.

4. A wave-guide coupling for two axially aligned wave-guide sections comprising a third axially aligned wave-guide section having electrically conductive fluid walls, a low-loss dielectric member closely fitted into the adjacent ends of said first two wave-guide sections, and an outer jacket encasing the adjacent ends of said wave-guide sections and maintaining the conducting iluid about the surface of said dielectric member exterior of said rst two wave-guide sections.

5. A variable length wave-guide coupling for joining two axially aligned wave-guide sections comprising a third axially aligned wave-guide section having electrically conductive fluid walls, a low-loss dielectric tube tapered at both its ends and having one end secured in one of said rst two wave-guide sections and the other end closely tted in slidable relation inA the other of said first two wave-guide sections, and an outer jacket encasing the adjacent ends of said Waveguide sections and maintaining the conducting fluid about the surface of said dielectric member exterior of said rst two wave-guide sections.

6. A wave-guide coupling for a pair of axially aligned wave-guide sections having like crosssections comprising a low-loss dielectric liner having an outer cross-section substantially the same as the inner cross-section of said waveguide sections, said dielectric liner being secured within one of said sections and mounted in close fitting slidable relation with the other of said sections, an outer jacket secured to the end of one of said sections and enclosing a portion of said other section, and a quantity of conductive uid maintained Within said jacket sufficient to cover the exposed outer surface of said dielectric liner and thereby provide an inner conducting surface continuous with and bridging the inner surfaces of the guide sections.

LESTER HOCHGRAF.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Johnson Dec. 30, 1947 

